Gemini 11 (officially Gemini XI)[2] was the ninth manned spaceflight mission of NASA's Project Gemini, which flew from September 12 to 15, 1966. It was the 17th manned American flight and the 25th spaceflight to that time (includes X-15 flights over 100 kilometers (54 nmi)). Astronauts Charles "Pete" Conrad, Jr. and Richard F. Gordon Jr. performed the first-ever direct-ascent (first orbit) rendezvous with an Agena Target Vehicle, docking with it one hour and thirty-four minutes after launch; used the Agena rocket engine to achieve a world record high-apogee earth orbit; and created a small amount of artificial gravity by spinning the two spacecraft connected by a tether. Gordon also performed two extra-vehicular activities for a total of 2 hours and 41 minutes.

Arabian Peninsula (top left) and northeast Africa (bottom) as seen from the orbiting Gemini-11 spacecraft at an altitude of 340 nautical miles during its 27th revolution of Earth. (Taken with a modified 70mm Hasselblad camera.)

The direct-ascent rendezvous and docking with the Agena vehicle was achieved approximately 94 minutes after lift-off, depending on the on-board computer and radar equipment with only minimal assistance from ground support.[4]

Gemini 11 used the rocket on its Agena target vehicle to raise its apogee to 853 miles (1,373 km), the highest Earth orbit ever reached by a manned spacecraft.[5] The perigee was 179 miles (288 km), and maximum velocity (at perigee) was 17,967 miles per hour (28,915 km/h).[4] The apogee record stands as of March 2016, even though men have achieved greater distances from Earth by flying to the Moon in the Apollo program.[6] The maximum operational altitude of the Space Shuttle was lower, at 380 miles (610 km).

The crew docked and undocked four times, and still had sufficient Gemini maneuvering fuel for an unplanned fifth rendezvous. They did not remain in the high orbit, but changed it back to a near-circular one at 184 miles (296 km).[4]

Gordon's first EVA, planned to last for two hours, involved fastening a 100-foot (30 m) tether, stored in the Agena's docking collar, to the Gemini's docking bar for the passive stabilization experiment. Gordon achieved this, but as with previous Gemini EVAs, trying to do work for an extended period proved more fatiguing than in ground simulation, and the EVA had to be terminated after only half an hour.

The passive stabilization experiment proved to be a bit troublesome. Conrad and Gordon separated the craft in a nose-down (i.e., Agena-down) position, but found that the tether would not be kept taut simply by the Earth's gravity gradient, as expected. However, they were able to generate a small amount of artificial gravity, about 0.00015 g, by firing their side thrusters to slowly rotate the combined craft like a slow-motion pair of bolas.[4]

Gordon successfully performed a second EVA standing up with his head and shoulders out of the hatch to photograph the Earth, clouds, and stars. This was not tiring, and lasted more than two hours.[4]

Mass Determination: To test a technique and accuracy of a direct contact method of determining the mass of an orbiting object, in this case the Agena Target Vehicle.

Night Image Intensification: To test the usefulness and performance of a low-light-level television system as a supplement to unaided vision in observing surface features primarily when such features are in darkness and spacecraft pilots are not dark-adapted.

Power Tool Evaluation: To evaluate man's capability to perform work tasks in space, including the comparison of ability to work tethered and untethered, and to evaluate the performance of the minimum reaction power tool.

Synoptic Weather Photography: To obtain selective high quality photographs of clouds to study the fine structure of the Earth's weather system.

Nuclear Emulsion: To study the cosmic radiation incident on the Earth's atmosphere, to obtain detailed chemical composition of the heavy primary nuclei, and to search for rare particles.

Airglow Horizon Photography: To measure by direct photography the heights at which atomic oxygen and sodium layers occur in the upper atmosphere.

Ultraviolet Astronomical Camera: To test the techniques of ultraviolet photography under vacuum conditions and to obtain ultraviolet radiation observations of stars in wavelength region of 2,000 to 4,000 Angstroms by spectral means.

Ion Wake Measurement: To determine and measure the ion and electron wake structure and perturbation of the ambient medium produced by an orbiting vehicle, and to study the changes in the ion flux and wake caused by thruster firings.

Earth-Moon Libration Region Photography: To investigate the regions of the L4 and L5 libration points of the earth-moon system to determine the possible existence of clouds of particulate matter orbiting the earth in these regions.

Dim-Light Photography and Orthicon: To obtain photographs of various faint and diffuse astronomical phenomena.

The mission ended with the first totally automatic, computer-controlled reentry by the U.S., which brought Gemini 11 down 2.8 miles (4.5 km) from its recovery ship USS Guam, only 1.5 miles (2.4 km) from the planned position.[4]

Since Conrad and Gordon were both members of the US Navy, the embroidered mission patch was designed in Navy colors: blue and gold. Stars are used to mark the major milestones of the mission. The first orbit Agena rendezvous is marked by a small gold star just above the Earth, to the left. The Agena docking is marked by a large star on the left. The star at the top marks the record high apogee reached by Gemini 11. Note that the scale is greatly exaggerated; their maximum altitude of 850 miles (1,370 km) is roughly the distance from St. Louis to Cape Kennedy. Finally, the star on the right marks Dick Gordon's spacewalk. The docking, record apogee and spacewalk are also shown on the patch by the Agena, orbital apogee path and spacewalking astronaut.

^However, if Apollo had progressed as planned, the record would have been broken by what was designated as the E mission which was a medium Earth orbital test of the complete Apollo spacecraft, with an apogee of 3,500 nautical miles (6,500 km) planned to be flown in March 1969. But the first Lunar Module was not ready in time for the D mission planned for December 1968, which was a low Earth orbit test (see List of Apollo mission types). Therefore, the E mission was cancelled and replaced with the D mission in March, and Gemini 11's apogee record stands.